Alzheimer's disease (AD) is the fourth most common cause of death in the U.S. after heart disease, cancer and stroke. It presently afflicts more than four million people and this number is expected to double during the next forty years as the population ages. There is presently no cure for AD and treatments are largely palliative rather than treating the underlying causes of disease. A stated aim of the National Institute of Aging is to delay the age of onset by five years during the next five years and by ten years within the next ten years thus reducing significantly the number of people affected by AD.
Apart from advanced age and Down syndrome the only consistent risk factor for the development of AD identified in epidemiological surveys has been the presence of a positive family history of disease. The most striking evidence in support of genetic factors is the existence, amongst early onset cases of AD, of families in which the disease is inherited as a fully penetrant autosomal dominant disorder (Nee et al., Arch. Neurol. 40:203-208). The existence of large families with an inherited form of AD has enabled a genetic linkage strategy to be used to localize the disease genes.
The observation of AD neuropathology in aging Down syndrome (DS) patients led researchers to analyze chromosome 21 in families with an inherited form of AD. Genetic linkage between FAD and markers on the long arm of chromosome 21 was first reported in 1987 (St. George-Hyslop, et al., Nature, 347:194-197. (1990)). Since that time it has been demonstrated that early onset FAD is genetically heterogeneous and that many pedigrees do not show linkage to chromosome 21 markers (St. George-Hyslop, et al., Nature Genetics, 2:330-334 (1992) and Schellenberg, et al., Annals Of Neurology 31:223-227 (1992)).
Genetic linkage studies have identified a second locus causing early onset FAD (herein "early onset Alzheimers Disease" or "EOAD") on the long arm of chromosome 14 (Schellenberg, et al., Annals Of Neurology 31:223-227 (1992); Van Broeckhoven, et al., Nature Genetics 2:335-339 (1992); St. George-Hyslop, et al., Nature Genetics, 2:330-334 (1992)) linkage was first reported to D14S43 and localized to a region of about 23cM between D14S52 and D14SS3. The isolation of additional genetic markers has led to the candidate region being narrowed to a distance of 6.4 cM between D14S289 and D14S61 (Cruts, et al., Human Molecular Genetics. A positional cloning strategy is presently being used in our tab and others to identify the defective gene. Although the majority of EOAD families studied show linkage to this locus, at least one more locus causing early onset FAD must exist because the Volga German families show recombination with the APP gene and the markers tightly linked to the FAD gene on chromosome 14 (Schellenberg, et al., Science 25:668-671(1992). Apart from age of onset of disease no phenotypic or neuropathological markers have been identified that distinguish between the different causes of FAD. Identification of new chromosome 14-linked families for meiotic mapping and the successful application of linkage disequilibrium techniques (both of which could narrow down the region of interest considerably) could be key factors in the rapid identification of this gene since 6.4 cM of DNA could contain hundreds of candidate genes.
When the AD3 locus was first localized to chromosome 14 two genes were known to map to this region of the chromosome: the heat shock protein, HSPA2 and the protooncogene cfos. Refinement in the mapping of HSPA2 and the identification of additional recombinants in AD families now place the HSPA2 gene outside the candidate region cfos remains within the candidate region. However, extensive sequencing of the coding region by several groups has failed to reveal any pathogenic mutations although several polymorphisms have been identified and physical characterization of the early onset Alzheimer's disease AD3 locus on chromosome 14q24.3. Two expressed sequence tagged sites (ESTs) have also been mapped just outside the candidate region: D14S1O 2E, which maps between D14S289 and D14S251 and D14S1O1E, which maps between D14S61 and D14S59. Two other genes and one pseudogene have been mapped within the candidate region. The known genes are transforming growth factor beta (tgf-.beta.), and the Kreb's cycle enzyme dihydrolipoamide succinyltransferase (DLST). Since tgf-.beta. is known to modulate APP expression it represents a plausible candidate gene. To date no mutations have been identified in this gene in patients from chromosome 14-linked FAD cases. A reduction in the activity of DLST has been reported in brains from AD cases and also in the fibroblasts from chromosome 14-linked AD cases. However, to date no mutations have been identified in this gene in patients from chromosome 14-linked FAD cases.
The amino acid sequence of a non-splice form of the EOAD protein was recently diclosed (Sherrington, Nature 375:754 (1995)). Neither the splice variant of the EOAD gene nor the full length gene sequence of the EOAD were disclosed.
There is a clear need for treatments for this disease and the present invention relates to compounds and methods of treatment. Moreover, identification of such EOAD has been hampered by the unavailability of convenient diagnostic materials and methods. Thus, there is also a need for a rapid, sensitive, and specific test to aid in the diagnosis of EOAD. DNA-based diagnostic tests not only are sensitive and specific but also have the advantage of being rapid. Early detection and identification of EOAD facilitate prompt, appropriate treatment and care. The invention includes embodiments which are DNA sequences that are unique to the EOAD gene and comprise nucleic acid mutations are useful as diagnostic probes to detect the EOAD or a predisposition for EOAD.
This invention provides a unique novel set of DNA sequences useful for the detection of EOAD gene mutations, and particularly useful as primers and probes for the detection of EOAD or a predisposition for EOAD.